Hey there, great to see a new face
I assume you found a Graphite vein with a few Diamond Ores arround Y=12. You probably cant mine the ore because it requires a better tool than you currently have.
Diamond Ore requires a pick with mining level of 3 or higher. That is no easy feat and requires some machinery. You can find a list of the materials and their mining levels here:
On first glance I would recommend a Cobalt Or a Gem Pick to mine your diamonds.
The "Small Ore" you found is something different. Small ores always drop dusts or crushed ores. Which means that unless you have a few relatively high tier machines, you wont get diamonds out of them.
But you shouldnt need diamonds that early anyways. Focus on finding Tin and Copper to make Bronze, you'll need A LOT of bronze to get your steel production going. Which you will need for your first machines.
Feel free to ask if something is unclear. Gregtech can be pretty overwhelming at first.
Thanks soo much!!!